This is a 35 USC 371 application of PCT/DE 00/00213 filed on Jan. 26, 2000.
The invention is based on a fuel injection system for an internal combustion engine, the fuel injection system having a high pressure pump which, in combination with two overpressure valves, supplies fuel to the injection system at different pressures.
One such fuel injection system is disclosed for instance in European Patent Disclosure EP 0 711 914 A1.
The use of fuel injection systems with pressure reservoirs is known in Diesel engines and in direct gasoline injection engine. These systems employ a high-pressure pump and sometimes a prefeed pump which prefeed pump supplies fuel at pressures of up to about 10 bar. Systems with intake throttle regulation are also known.
In the injectors for the injection of the Diesel fuel, a distinction is presently made between stroke- and pressure-controlled systems. In a pressure-controlled fuel injection system, a valve body (such as a nozzle needle) is opened by the fuel pressure in the nozzle chamber of the injector counter to the action of a closing force, and a nozzle opening is thus uncovered for an injection of the fuel. In a stroke-controlled fuel injection system, the opening and closing of the injection opening is effected with the aid of a valve body on the basis of the hydraulic cooperation of two fuel pressures in the nozzle chamber and in a control chamber. The pressure at which fuel emerges from the nozzle chamber into the cylinder is called the injection pressure, while the pressure at which the fuel is available or is stored in the injection system is called the system pressure. As for the injectors, there are also injection nozzles with a variable injection port cross section (vario-nozzle) and with a two-stage nozzle needle stroke.
In the pressure-controlled injection system known from EP 0 711 914 A1, fuel is compressed with the aid of a high-pressure pump to a first, high system pressure of about 1200 bar and stored in a first pressure reservoir. The fuel at high pressure is also fed into a second pressure reservoir, in which by regulation of its fuel delivery by means of a 2/2-way valve, a second high system pressure of approximately 400 bar is maintained. Via a valve control unit, then either the lower or the higher system pressure is carried into the nozzle chamber of an injector. There, a spring-loaded valve body is lifted from its valve seat by the pressure, so that fuel can emerge from the nozzle opening.
In this injection system, the high-pressure pump generates a pressure level and quantity of fuel which is above the maximum required for full-load of the engine. This high pressure fuel is supplied to a first reservoir. A pressure limiter or regulator is positioned at the first high pressure reservoir, and regulates the pressure thereof to maintain pressure at this stage at about 800 to about 1800 bar. This first reservoir is called the second high-pressure stage due to its being the higher of the pressures of the system. The first regulator releases the excess quantity of fuel into a second pressure reservoir. This second reservoir is maintained at about 200-1000 bar by a second regulator, which is positioned between this second reservoir and the fuel tank. Fuel in this second reservoir is said to be in the first stage because the pressure is lower than that of the second stage.
The pressure of the first high-pressure stage, which is maintained preferably at approximately 200 bar, can be utilized to enable a hydraulic valve adjustment of the inlet and outlet valves, an adjustment of the camshaft association, an actuation of engine braking systems, and so forth. Also with the pressure of the first high-pressure stage, a preinjection and/or a postinjection can be achieved.
For certain applications, such as in Otto engines, a hydraulic pressure step-up from lubricating oil to fuel, or vice versa, can be done selectively from the first and second high-pressure stages. There is also the capability of using the pressure from the first high-pressure stage to control the opening cross section or to trigger injection nozzles under stroke or pressure control. The control of the stroke can be done quite simply via. pressure/travel against a spring force or via a fixed stop. The pressures can be switched via piezoelectric or magnet valves, and the control pressure for all the cylinders can be switched either centrally via one valve or locally via a plurality of valves. For triggering the injection nozzles, their leaking oil line is optionally also suitable. With this control pressure of the first high-pressure stage, a vario-nozzle can for instance also be triggered. The system is suitable for both Otto and Diesel engines.
The fuel injection system of the invention furthermore enables the following:
control of systems present in the engine, such as inlet and outlet devices, via the fuel system.
a compact structure. Piezoelectric or magnet valves can be provided on the pressure reservoir or pressure reservoirs and need not be disposed directly in or on the nozzle holder in the cylinder head.
triggering of injection nozzles under pressure or stroke control and which can be infinitely variably, or alternatively can be controlled or via a stroke stop, regardless of the injection pressure.
low amount of electrical power only be used for actuating piezoelectric or magnet valves, since low control pressures and short travel distances are possible.
a modular design.
the system allows for varying injection onset, and both preinjection and postinjection are therefore possible.
the use of the pressure of the first high-pressure stage for a preinjection and/or postinjection. Because of the low injection pressure, soot development and oil thinning are largely avoided.